Stabilized chlorinated hydrocarbon compositions



United States Patent 2 Claims. 61460-6525 The present invention relates to a process for the stabilization of chlorinated hydrocarbons, particularly trichlorethylene and perchlorethylene, in order to avoid decomposition of these products and the simultaneous formation of oxidation products during manufacture, storage or use.

It is known that, under the influence of heat and oxygen, chlorinated hydrocarbons undergo an oxidation which is catalysed by different agents such as light and certain metallic salts, in particular salts of iron, aluminum and magnesium.

To retard this oxidation it has been proposed to add to these chlorinated hydrocarbons small quantities of various individual products, such as phenols, alcohols, epoxy compounds, inorganic or organic basic products and so forth. The use of phenols in particular has been indicated in U.S. Patent No. 2,008,680 and German Patent No. 573,105 and the use of alcohols in U.S. Patent No. 2,371,644.

It is also known to add two or more stabilizers which exert a synergistic action. Thus, for example,our U.S. Patent No. 2,935,537 covers the simultaneous use of phenol and an epoxy compound, and that of aniline, pyrrole or a derivative of pyrrole. Other patents cover the simultaneous use of a pentanol and a nitrogen base (US. Patent No. 2,966,424), of phenol and an alcohol (U.S. Patent No. 2,878,518), or of a phenolic compound and an epoxy compound having in the molecule another oxygen-containing function (U.S. patent application Serial No. 314,650, now U.S. Patent No. 3,260,760).

The applicants have now found that a very significant synergistic effect can be obtained for stabilizing chlorinated hydrocarbons by using small quantities of mixtures comprising at least two different phenolic compounds of which the first is selected from hydroxybenzene, alkylsubstituted derivatives thereof, pyrocatechol (orthodiphenol) or the alkyl-subistituted derivatives of the latter, and of which the other phenolic compound or compounds are selected from pyrocatechol, its valkyl-substituted derivatives and the ortho-alcohol-phenols.

Examples of alkyl-substituted derivatives of hydroxy benzene are the cresols and thymol. Of the alkyl-substituted derivatives of pyrocatechol particular mention may be made of p-tertiary-butylcatechol .and p-methylcatechol. An example of an ortho-alcohol-phenol is s aligenol.

The stabilizing action of various compounds and systems of compounds used to improve the resistance of the chlorinated hydrocarbons to decomposition has been shown by various experiments. Some of these have consisted of an accelerated test in the laboratory carried out in the following manner.

Patented Dec. 20, 1966 150 cc. of trichl-orethylene, for example, and a test piece of aluminum, are placed in a 300 cc. flask in an apparatus of the Soxhlet type provided with a cc. extractor. The flask is electrically heated and the trichlorethylene is rapidly brought to boiling under reflux at a constant rate while the apparatus is swept by a current of oxygen and illuminated by a fluorescent lamp of the blue actinic type. During the whole test, the rate of release of acid vapours is measured at the outlet of the apparatus. This rate, very low at first, suddenly becomes very high while the trichlorethylene darkens and changes intoa black gummy mass. The resistance of the trichlorethylene to the test is measured by the'time in hours counted from the start of the experiment, when the sample has reached boiling, until the moment when the release of acid suddenly becomes very rapid and exceeds 15.10" gr. mol/hr.

The following Table 1 shows the resistance to decomposition of trichlorethylene Which has not been stabilized, and of trichlorethylene stabilized by phenolic compounds the combined use of which forms the object of the present invention.

The results show that the use of a combination of a phenol or an orthodiphenol with pyrocatechol or one of its alkyl-substituted derivatives gives a clear synergistic action, since the resistance to oxidation of the trichlor ethylene treated by a mixture of these compounds is very clearly superior to the total of the effects obtained by the sole use of each of the constituents.

The improvement of the chlorinated hydrocarbons treated according to the invention can be further shown by applying the well known United States Federal Specification No. O-T-634a, Type II. It may be recalled that this test is carried out as follows. The sample of chlorinated hydrocarbon to be tested is placed in an Erlenmeyer flask heated by an electric lamp and surmounted .by a condenser; a test piece of SAE 1020 steel is suspended above the liquid in the vapour stage and another test piece is placed at the bottom of the flask, that is to say in the liquid phase. Oxygen saturated with water is then continuously introduced for 48 hours, the introduction being effected at the rate of 10 to 12 bubbles of oxygen per minute. At the end of the test acidity of the chlorinated hydrocarbon is determined in the presence of a coloured indicator; in the tests carried out by us, phenolphthalein prescribed as indicator in the federal specification, was replaced by bromocresol green which is not sensitive to the acidity of carbon dioxide gas. The acidity calculated as'HCl, is expressed in percent by weight of chlorinated hydrocarbon.

The following Table 2 gives some results obtained by applying this technique.

TABLE 2.TESTS ACCORDING TO FEDERAL SPECIFIOA. TION O-T-634a-II (U.S.A.)

Designation of Acidity tests and Quantity and composition of after test corresponding products tested (H 01 persolutions cent by weight) 200 cc. of trichlorethylene containing 0. 0005 pyrocateohol at rate of 5 mg./l. 200 cc. of triohlorethylene containing 0. 0005 p-cresol at rate of 150 mg./l. 1023 cc. of solution A+100 cc. of solution 0. 00035 D 200 cc. of trichlorethylene containing 0. 0005 p-tertiary butyloatechol at rate of 25 mg. E 200 cc. of trichlorethylene containing 0. 0005 p-oresol at rate of 150 mg./l. F %ceof solution D+100 cc. of solution 0. 00025 G 50 of solution D+l50 cc. of solution 0. 00015 H 150Ecc. of solution D+50 cc. of solution 0. 00015 I 200 cc. of trichlorethylene containing 0.00625 saligenol at rate of 200 mg. ll. J 200 cc. of trichlorethylene containing 0. 0063 phenol at rate of 200 mg./l. K 60 cc. of solution I+140 cc. of solutionl 0. 00335 L 140 cc. of solution I+60 cc. of solution J 0. 0035 Here again the results show the synergistic efiect obtained by the use of the combinations according to the invention; it is sufiicient to compare test C with tests A and B, tests F, G and H with tests D and E and tests K and L with tests I and J to establish that the mixtures of stabilizing compounds give an acidity lower than that obtained by each of the constituents taken separately.

The quantities of stabilizing materials to be used lie generally between 0.002 to 0.5 gr./l. for each of the phenolic compounds.

If desired, one may add to the combination of stabilizing substances forming the object of the invention, other known compounds, in particular inorganic or organic substances having an alkaline reaction which modify the initial pH value of the chlorinated hydrocarbon. The mixture of phenolic compounds can in particular replace the single phenol used in the known synergistic compositions, such as those which form the object of our US. patent application Serial No. 314,650 already mentioned and comprise a phenol associated with an epoxy compound having another oxygen-containing function in the molecule.

The stabilizing compositions according to the invention are particularly effective for stabilizing trichlorethylene and perchlorethylene. They can also be used for stabilizing other chlorinated hydrocarbons such as chloromcthanes, dichloroethanes, trichloroethanes, dichloroethylenes, allyl chloride, chloropropanes, chloropropenes, etc., and mixtures thereof.

We claim:

1. A chlorinated hydrocarbon containing, for the stabilization of the chlorinated hydrocarbon against oxidation, a synergistic mixture comprising at least two difierent phenolic compounds each in a concentration of 0.002 to 0.5 gram per liter of chlorinated hydrocarbon, a first of said phenolic compounds being selected from the group consisting of phenol, p-cresol, pyrocatechol, p-methylcatechol and p-tertiary-butylcatechol and a second of said phenolic compounds being selected from the group consisting of pyrocatechol, p-methyleatechol and p-tertiarybutylcatechol.

2. A chlorinated hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene, said chlorinated hydrocarbon containing, for the stabilization of the chlorinated hydrocarbon against oxidation, a synergistic mixture comprising at least two different phenolic compounds each in a concentration of 0.002 to 0.5 gram per liter of chlorinated hydrocarbon, a first of said phenolic compounds being selected from the group consisting of phenol, p-cresol, pyrocatechol, p-methylcatechol and p-tertiary-butylcatechol and a second of said phenolic compounds being selected from the group consisting of pyrocatechol, p-methylcatechol and p-tertiarybutylcatechol.

References Cited by the Examiner UNITED STATES PATENTS 2,958,712 11/1960 Starks 260-652.5

FOREIGN PATENTS 209,884 6/1960 Austria.

BERNARD HELFIN, Primary Examiner.

LEON ZITVER, Examiner.

M. M. JACOB, Assistant Examiner. 

1. A CHLORINATED HYDROCARBON CONTAINING, FOR THE STABILIZATION OF THE CHLORINATED HYDROCARBON AGAINST OXIDATION, A SYNERGISTIC MIXTURE COMPRISING AT LEAST TWO DIFFERENT PHENOLIC COMPOUND EACH IN A CONCENTRATION OF 0.002 TO 0.5 GRAM PER LITER OF CHLORINATED HYDROCARBON, A FIRST OF SAID PHENOLIC COMPOUNDS BEING SELECTED FROM THE GROUP CONSISTING OF PHENOL, P-CRESOL, PYROCATECHOL, P-METHYLCATECHOL AND P-TERTIARY-BUTYLCATECHOL AND A SECOND OF SAID PHENOLIC COMPOUNDS BEING SELECTED FROM THE GROUP CONSISTING OF PYROCATECHOL, P-METHYLCATECHOL AND P-TERTIARYBUTYLCATECHOL. 